The main purpose of Japan's first lunar surface mission was to demonstrate precision lunar landing. During its descent the lander recognized lunar craters by applying technology from facial recognition systems, and determined its current location from utilizing observation data collected by the SELENE (Kaguya) lunar orbiter mission. SLIM aimed to soft land with an accuracy range of 100 m (330 ft).[6][9][10] In comparison, the accuracy of the 1969 Apollo 11Eagle lunar module was an elliptic which was 20 km (12 mi) long in downrange and 5 km (3.1 mi) wide in crossrange.[2]
According to Yoshifumi Inatani, deputy director general of the JAXA Institute of Space and Astronautical Science (ISAS), succeeding in this extremely precise landing will lead to enhanced quality of space exploration.[11] The expected cost for developing this project is 18 billion yen, or US$121.5 million.[12]
History
The proposal which later came to be known as SLIM existed in 2005, as the Small Lunar Landing Experiment Satellite (小型月着陸実験衛星).[13] On 27 December 2013, ISAS called for proposals for its next "Competitively-Chosen Medium-Sized Focused Mission", and SLIM was among the seven proposals submitted.[2] In June 2014, SLIM passed the semi-final selection along with the DESTINY+ technology demonstration mission, and in February 2015 SLIM was ultimately selected.[14] From April 2016, SLIM gained project status within JAXA.[15] In May 2016, Mitsubishi Electric (MELCO) was awarded the contract for building the spacecraft.[16]
SLIM was not the first Japanese lunar lander built for operation on the Moon's surface; on 27 May 2016 NASA announced that the OMOTENASHI (Outstanding Moon exploration Technologies demonstrated by Nano Semi-Hard Impactor) CubeSat lander jointly developed by JAXA and the University of Tokyo was to be launched as a secondary payload on Space Launch System (SLS) Artemis 1. OMOTENASHI was meant to deploy a mini lunar lander weighing 1 kg; however, on November 21, 2022, JAXA announced that attempts to communicate with the spacecraft had ceased due to the solar cells failing to generate power because they were facing away from the Sun.[17] They wouldn't face the sun again until March 2023.[18]
In 2017, because of funding difficulties arising from XARM (XRISM)'s development cost, SLIM's launch was switched from a dedicated Epsilon flight to a rideshare H-IIA flight.[19] The resulting cost savings will be transferred to develop other satellites that are behind schedule due to XRISM.[19]
Rovers
Lunar Excursion Vehicle 1
Lunar Excursion Vehicle 1 (LEV-1) is a lunar rover which will move using a hopping mechanism. The hopper has direct-to-Earth communication equipment, wide-angle visible light cameras (2), small electric equipment and UHF band antennas taken from MINERVA and OMOTENASHI.[20]
Science Payloads:
Thermometer
Radiation monitor
Inclinometer
Lunar Excursion Vehicle 2
Lunar Excursion Vehicle 2 (LEV-2) or SORA-Q [ja], is a tiny rover developed by JAXA in joint cooperation with Tomy, Sony Group, and Doshisha University, which had been mounted on SLIM.[21] The rover has a mass of 250 g and is equipped with two small cameras. LEV-2 can change its shape to run on the lunar surface for about two hours.[22] It is the second rover of its kind to attempt operations on the lunar surface; the first was on Hakuto-R Mission 1, which crashed before the lander could be deployed.[23][24]
Mission
SLIM was successfully launched together with the X-Ray Imaging and Spectroscopy Mission (XRISM) space telescope on 6 September 2023 at 23:42 UTC (7 September 08:42 Japan Standard Time)[3] planning to land near Shioli crater (13.3°S, 25.2°E) via weak stability boundary like trajectory.[25] SLIM entered lunar orbit 25 December JST.[26]
The lander touched at the Sea of Nectar (circled)
The lunar lander, nicknamed Moon Sniper for its extremely accurate landing precision within the projected 100 meters (330 ft) long landing ellipse, touched down onto the Moon on 19 January 2024 at 15:20 UTC, at the Sea of Nectar, south of the Theophilus crater. Japan thus became the fifth nation to successfully soft land an operational spacecraft on the Moon, after the Soviet Union, United States, China, and India.[27][28][29]
Although SLIM landed successfully, the lander suffered a technical issue with its solar panels, which became oriented westwards facing opposite the Sun at the start of lunar day, thereby failing to generate enough power.[30] The lander was able to operate on internal battery power for a short period of time, but was manually powered down on 19 January 2024 at 17:57 UTC (20 January 02:57 Japan Standard Time) to prevent over-discharge of the battery.[17] The mission's operators hope that the lander will wake up after a few days when sunlight should hit the solar panels.[31]
The two LEV 1 and 2 rovers, deployed while the lander was hovering just before it touched down, are working as planned, with LEV-1 communicating independently to ground stations.[31]
^"Archived copy"(PDF). Archived(PDF) from the original on 8 September 2023. Retrieved 25 August 2023.{{cite web}}: CS1 maint: archived copy as title (link)
^Hashimoto, Tatsuaki (30 November 2005). "小型月着陸実験衛星"(PDF) (in Japanese). Archived from the original(PDF) on 5 March 2016. Retrieved 22 June 2016.
^"深宇宙探査技術実証機 DESTINY+"(PDF) (in Japanese). 7 January 2016. Archived(PDF) from the original on 28 January 2022. Retrieved 23 June 2016.
^"ISASニュース 2016.5 No.422"(PDF) (in Japanese). Institute of Space and Astronautical Science. 27 May 2016. Archived(PDF) from the original on 11 April 2023. Retrieved 23 June 2016.
Launches are separated by dots ( • ), payloads by commas ( , ), multiple names for the same satellite by slashes ( / ). Crewed flights are underlined. Launch failures are marked with the † sign. Payloads deployed from other spacecraft are (enclosed in parentheses).
